A souterrain is an underground passage or chamber, typically built during the early medieval period in Ireland, often used for storage, refuge, or both. Here, the ground has settled inward where the roof of such a structure may have given way over the centuries, leaving the surface pocked with two subtle hollows that are easy to miss unless you know what you are looking at.

The rath itself, a circular earthwork enclosure of the kind that was the standard farmstead unit of early medieval Ireland, has been recorded in the area. Souterrains were commonly built within or adjacent to raths, constructed from dry-stone walling and roofed with large lintels, then covered over with earth. When the roofing stones eventually fail, the infill collapses, and the result is precisely the kind of gentle surface depression visible here. The site at Caher has not been excavated, and the souterrain remains unconfirmed, its presence inferred from those two quiet dips in the ground rather than from any direct investigation.